analysis of trophic gradient through environ-mental filter influencing ... · pdf fileanalysis...

J. Bio. & Env. Sci. 2014

218 | Chakrabarty and Homechaudhuri

RESEARCH PAPER OPEN ACCESS

Analysis of trophic gradient through environ-mental filter

influencing fish assemblage structure of the river Teesta in

Eastern Himalayas

Munmun Chakrabarty, Sumit Homechaudhuri*

Aquatic Bioresource Research Laboratory, Department of Zoology, University of Calcutta, 35,

Ballygunge Circular Road, Kolkata-700019, India

Article published on April 18, 2014

Key words: Hill-stream, ichthyofauna, dietary composition, feeding guild, niche filter.

Abstract

Factors controlling biodiversity and co-existence of species need immediate attention to maintain biodiversity.

Co-existence between interacting species is based on their ecological niches or functional roles and can be

assessed by niche assembly theory and construction of trophic guild. In the present study, the diet composition of

fishes have been analyzed both qualitatively and quantitatively to describe feeding patterns along environmental

gradient towards linking biodiversity with functional diversity patterns to shape species assemblage. We

evaluated the trophic guild structure of 92 fish species of the large, torrential river Teesta (within West Bengal)

having its origin in eastern Himalayas. Stomach contents of 1515 fish specimens have been analyzed and fishes

were ascertained 14 different trophic guilds. Canonical correspondence analysis was performed to study species

associations with environmental parameters. Preliminary analysis showed a dietary shift of the respective fish

assemblages from high to low altitude from specified feeders (aquatic insectivores) to omnivorous respectively.

Aquatic insect larvae formed the most important prey in general, especially in high altitude zone followed by

algae. The dietary preferences indicate that fish assemblage pattern seems to be guided by niche breadth and

environment acting as the main filtering agent towards species sorting and survival. This study is an important

step in structuring fish community of the River Teesta and to lay the foundation for subsequent future efforts on

the conservation of aquatic communities and their feeding habitats.

*Corresponding Author: Sumit Homechaudhuri [email protected]

Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220-6663 (Print) 2222-3045 (Online)

Vol. 4, No. 4, p. 218-232, 2014

http://www.innspub.net

mailto:[email protected]



Introduction

The Eastern Himalayan Biodiversity Hotspot region

and its foothills are very rich; especially the piscine

diversity and their populations inhabiting these areas

are numerous in variety and taxonomically

interesting. As such, the northern districts of West

Bengal, India especially the districts of Darjeeling and

Jalpaiguri, lying within the Eastern Himalayan

biodiversity hotspot range, hold a great importance

faunistically. The chief rivers are Mahananda and

Teesta with many tributaries like Murti, Atrai,

Jaldhaka, Karala, Karotoyar, etc. The Himalaya is the

source of all major river systems in India. Like other

Himalayan rivers, Teesta river and its tributaries

provide a fair ecological niche for many indigenous

and a few exotic fish species. However, there is a lack

of baseline information on freshwater fish species

distributions and their ecological requirements

throughout the Eastern Himalayas. It was found that

31.3% of the 1,073 freshwater species of fishes,

molluscs, dragonflies and damselflies currently

known in the Eastern Himalaya region are assessed as

Data Deficient, emphasizing the urgent need for new

research in the region (Allen et al., 2010). These

augmented research of freshwater fish species in this

region and their various ecological implementations

towards evaluating their functional traits leading

towards assessment of aquatic environment health.

Alterations in water quality or habitat conditions

usually lead to variations in the availability of food

resources. Fish generally display high diet flexibility

and both temporal and spatial variations in their diets

(Abelha et al., 2001; Dekar et al., 2009). However, in

highly specific and also in disturbed environments,

experiencing alterations of water flow and available

substrates, these patterns can be altered, and changes

like increase in generalist species and reduced

numbers of trophic guilds can occur (Casatti et al.,

2006; Casatti et al., 2009).

In recent years, rapid radial expansion of urban

habitats and increased human interferences in the

natural environmental conditions of River Teesta

might lead to its obvious degradation in near future.

Moreover, hydropower dams construction at various

levels of the river could potentially decrease its faunal

composition. Till date scanty work has been

undertaken to study the fish assemblage of River

Teesta and their various ecological implications. In

context, evaluation in variations in the trophic

organization of ichthyofaunal assemblages can be

considered to be indicators of changes in the quality

and complexity of a habitat (Karr, 1981). Considering

niche filtering hypothesis, which assumes that at local

scale species assemblages can be regulated both by

abiotic and biotic interactions acting simultaneously

with environmental conditions (abiotic properties of

the habitat) acting as a filter causing only a bottle

neck population to survive (Zobel, 1997; Mouillot,

2006), we propose to evaluate how the origin and use

of food resources varied spatially across the riverine

stretch. Therefore, we aimed to describe the diet of

the fish assemblages in a hill stream river, Teesta in

West Bengal (originating in the Eastern Himalayan

biodiversity hotspot region) to evaluate the use of

food resources of the resident fish species and

whether and how they varied across different

environmental gradient and to seek assembly rules

based on functional traits.

Material & methods

Study area

River Teesta, originating from north Sikkim and

carving out verdant Himalayan temperate and tropical

river valleys, traverses the Indian states of Sikkim and

West Bengal and finally descends to Brahmaputra in

Bangladesh. The total length of the river is 309 km

(192 mi), draining an area of 12,540 Km2. The present

study area includes the course of the River Teesta in

West Bengal (Fig. 1) divided into ecological zones based

on elevation gradient and habitat types. The river

stretch was divided in four zones (Table. 1) viz. the

upper stretch (Rishi khola and Rungpo) where

elevations is higher with low temperatures; middle

stretch (Teesta Bazaar) with low elevation; at Sevoke

the river hits the plains; lastly the river plains

(Gojoldoba, Domohoni and Haldibari). Fish sampling

was performed at regular intervals at seven sites along



the longitudinal stretch of the river in West Bengal covering a distance of 99.28 km.

Table 1 Habitat types of the sampling zones along longitudinal gradient of River Teesta in West Bengal.

Fish Zones

Sites Elevation Riparian

vegetation Predominant substrate

High-Mid altitude zone

Rishi Khola

Moderate to high elevation watersheds dominated by side slopes with gentle slopes and steep slopes.

Primary forest; hilly terrain.

Rocky Predominantly rocky along with sandy stretches

Rungpo Secondary forest.

Mid altitude zone

Teesta Bazaar

Moderate to high elevation watersheds dominated by side slopes and gentle slopes.

Secondary forest; ongoing construction work of Teesta Barrage project.

Sandy stretches with pebbles, partly rocky

Low altitude-plain zone

Sevoke

Moderate to low elevation watersheds dominated by gentle slopes with substantial areas of flats and sideslopes; river hits the plain at this site.

Secondary forest Sandy with pebbles and stones

River plains

Gojoldoba

Low elevation dominated by flats, pastured land and

urban inhabitation.

Secondary forest; Urban area; presence of Teesta Barrage

Few stretches with pebbles, mostly muddy

Domohoni

Agriculture land; Urban area

Haldibari Agriculture land; Urban area

Fig. 1 River Teesta Catchment area in West Bengal.

Sampling

Fish sampling was carried out from December 2010

to March 2013 at 7 sites under 4 environmental zones

following a transverse transect intended to give a

representative sample of all mesohabitat types along

the longitudinal gradient of River Teesta at Darjeeling

and Jalpaiguri districts in West Bengal. All the

important freshwater aquatic microhabitats (riffles,

pools, cascade, falls, etc.) were sampled using gill

nets, cast nets, dragnets, and hooks and lines of

varying dimensions. Captured fish specimens were

fixed in 10% formalin solution and, after 48 h,

transferred to a 70% Ethyl alcohol solution. Fishes

were identified to the lowest taxonomic level (Shaw

and Shebbeare, 1937; Day, 1889; Talwar and

Jhingran, 1991; Jayaram, 2006, 2010; Menon, 1987).

All specimens have been deposited in the fish



collection repertoire at the Zoological Survey of India,

Kolkata.

Food and Intestine length analysis

For 92 of the identified species, sub-samples were

used for diet analysis. Stomach contents of two to ten

fish specimens were examined in each species (1515

specimens). After drying the fish between two pieces

of tissue paper the body mass and standard length of

each preserved specimen was measured to the nearest

0.01 g using an electronic balance. Guts were

dissected under a binocular microscope and then

preserved in 70% ethanol. In species, mostly

cyprinids, which do not have a discrete stomach, the

anterior third of the intestine was dissected.

Specimens in which the stomach (anterior third of

intestine in cyprinids) contained no food items were

categorized as empty. The contents of each gut were

examined under a dissecting microscope using

reflected light and each item identified and assigned

to broader taxonomic groups (Merona et al., 2005).

Each prey item was then allocated to one of a number

of taxonomic groups, subsequently referred to as

dietary categories. The frequency of occurrence of

each dietary category in the gut of each fish (%F) was

recorded (Lima-Junior and Goitein, 2001).

Dietary analysis

To analyze how the diets of the fishes are related to

temporal variations in habitats, we used the statistical

package PRIMER-E v 6.0 (Clarke and Gorley, 2001).

Similarity matrices between samples were

constructed using the Bray-Curtis index (Legendre

and Legendre, 1998) and data were standardized (as

percentage) to minimize discrepancy between

samples. To examine the relative extents to which the

dietary compositions of fish were influenced overall

by differences among species and habitat type, the

percentage frequency and volumetric contributions of

the various dietary categories in the guts of each

species in each habitat type were first allocated into

groups of ten. The mean percentage frequency

contributions of the various dietary categories in each

group (¼ dietary sample) were then calculated and

square-root transformed. These values were used to

construct a Bray-Curtis similarity matrix, which was

subjected to non-metric multidimensional scaling

(MDS) ordination and one-way analyses of

similarities (ANOSIM) (Clarke and Gorley 2001;

Hourston et al. 2004) to evaluate whether habitat

type significantly influence dietary regime and

resource optimization and if so which is the most

favourable condition for optimum resource

utilization/partitioning. The magnitudes of the global

R-statistic values in the ANOSIM test (which typically

range from 1 when the composition of all samples

within each group are more similar to each other than

to any of the samples from any other group,

downwards to 0 if the average similarities between

and within groups are the same), were used to

ascertain the relative extent to which the dietary

compositions differed among species in respective

habitat types (Clarke, 1993). The significance level (P)

was recorded only for the most influential of those

factors and where that value was less than 5%.

SIMPROF ('similarity profile') test was performed, in

which the biotic similarities from a group of a priori

unstructured samples are ordered from smallest to

largest, plotted against their rank (the similarity

profile), and this profile compared with that expected

under a simple null hypothesis of no meaningful

structure within that group (Clarke et al., 2008).

Environmental data analysis

At each site, the following physical parameters of the

stream were measured at 2-3 points each 1feet apart-

a) stream depth, b) stream width, stream velocity, d)

air and water temperature, e) water pH, f) water

conductivity and g) Turbidity. CCA was conducted

using CANOCO (version 4.5) software packages

where the relative contribution of the ordination axes

was evaluated by the canonical coefficients between

the environmental variable and the fish assemblage

pattern based on their feeding habits. The species–

environment correlation is a measure of the

association between species and the environmental

variable (Ter Braak and Verdonschot, 1995).



Results

Composition and % occurrence of different dietary

components

The gut contents of individual fish species showed

that they mainly consumed 10 types of food items. On

analysis of cumulative frequency of the food

categories (Table. 2) obtained from gut analysis of the

individual fish species expressed as percentage at

respective altitude zones it was observed that majority

of the fish species consumes aquatic invertebrates.

The most consumed types of items were aquatic

insect larvae (36% of the total resources consumed) in

the high-mid altitude zones followed by algae (23% of

the total resources consumed) which was consumed

by 40% and 20% of species respectively. Whereas, in

the river plains various food resources were optimally

consumed resulting in the majority of omnivorous

forms which was consumed by 29 % of the species

and detritivores (23% of the total resources

consumed). Feeding guilds were developed based on

the major diet constituent of individual species and

each species were ascertained to 14 dietary categories

recognized in this study: Aquatic invertevore that

comprised mainly of Ephemeropteran, Chironomidae

and Hemipteran larvae, annelid and arachnid

remains; Algivore comprising filamentous algae and

vascular plant material; Detritivore that includes

unidentified material and also mineral material

including sand and gravel; Herbivore; Insectivore;

Macro-carnivore; Micro-carnivore; Omnivore;

Planktivore with high proportions of zoo/phyto

planktons and five rest mixed groups that shared

different food habits, viz., Micro-

carnivore/Insectivore, Planktivore/ Aquatic

Invertevore, Herbivore/ Detritivore, Insectivore/

Algaevore and Insectivore/ Detritivore (Fig. 2).

Table 2. Frequency (%F) of occurrence of recognized dietary categories of the gut of each species at respective

habitat zones

Altitudinal zones

Species LV FR HR AL TI PL CR AI FI DU

High-Mid altitude

zone

Psilorhynchus sucatio (Psu)

(Hamilton 1822) 0 0 0 80.5 0 0 0 5.5 0 14

Psilorhynchus balitora (Pb) (Hamilton, 1822)

0 0 0 75.5 0 0 0 7.5 0 17

Puntius terio (Pt)

(Hamilton, 1822) 0 0 0 75.5 0 0 0 7.5 0 17

Devario aequipinnatus (Da) (McClelland, 1839)

0 0 0 0 15.2 0 17.5 59.2 0 8.1

Schistura devdevi (Sd) Hora, 1935 0 0 0 10.2 20.2 0 1.6 60.2 0 7.8

Schistura savona (Ss) (Hamilton, 1822) 0 0 0 9.5 16 0 2.1 61.2 0 11.2

Danio rerio (Dr) (Hamilton, 1822) 0 0 0 0 10.6 0 15.2 63.5 0 10.8

Amblyceps mangois (Amg) (Hamilton, 1822)

0 0 0 0 0 0 19.8 58.5 0 21.7

Channa marulius (Cm)

(Hamilton, 1822) 0 0 0 0 25.2 0 0 45.2 0 29.6

Macrognathus pancalus

(Mp) Hamilton 1822. 0 0 0 15.3 0 0 0 45.2 0 39.5

Tor tor (Tt)

(Hamilton 1822) 12.3 0 9.5 40.3 0 0 0 0 0 37.9

Schizothorax richardsonii (Sr)

(Gray 1832) 0 0 0 0 0 39.5 0 45.3 0 15.2

Neolissochilus hexagonolepis (Nh) (McClelland, 1839)

0 0 0 60.2 7.5 0 0 15.3 0 17

Barilius barila (Bba)

(Hamilton, 1822) 17.2 0 19.5 0 0 13.9 0 29.1 0 20.3

Olyra kempi (Ok)

Chaudhuri, 1912 0 0 0 5.2 39.8 0 0 40.2 0 14.8

Badis badis (Bd)

(Hamilton, 1822) 0 0 10 0 0 0 29.5 31.6 0 28.9



Altitudinal zones


Mid altitude

zone

Barilius barila (Bba) (Hamilton, 1822) 17.2 0 19.5 0 0 13.9 0 29.1 0 20.3

Barilius barna (Bbr) (Hamilton 1822) 0 0 0 0 0 0 0 79.2 0 20.8

Barilius bendelisis (Bbe) (Hamilton, 1807)

19.2 0 17.5 0 0 15.6 0 24.5 0 23.2

Barilius shacra (Bs)

(Hamilton 1822) 11.5 0 18.2 0 0 14.3 0 26.4 0 29.6

Barilius vagra (Bv) (Hamilton, 1822) 13.5 0 19.2 0 0 16.1 25.6 0 25.6

Crossocheilus latius latius (Cl) (Hamilton, 1822)

2.5 5.6 0 10.2 0 61.8 0 0 0 19.9

Danio dangila (Dd) (Hamilton, 1822) 0 0 0 10.2 0 0 0 70.2 0 19.6

Danio rerio (Dr)

(Hamilton, 1822) 0 0 0 0 10.6 0 15.2 63.5 0 10.8

Garra annandalei (Ga) (Hora, 1921) 0 0 0 87.6 0 0 0 0 0 12.4

Garra gotyla gotyla (Ggg) (Gray, 1830)

0 0 0 79.5 0 0 0 0 0 20.5

Garra lamta (Hl)

(Hamilton, 1822) 0 0 0 81.2 0 0 0 0 0 18.8

Neolissochilus hexagonolepis (Nhg) (McClelland, 1839)

0 0 0 60.2 7.5 0 0 15.3 0 17

Neolissochilus hexastichus (Nhx) (McClelland 1839)

0 0 0 65.2 9.5 0 0 10.3 0 15

Schizothorax richardsonii (Sr) (Gray 1832)

0 0 0 0 0 39.5 0 45.3 0 15.2

Acanthocobitis botia (Ab) (Hamilton, 1822)

0 0 0 12.5 0 0 10.5 60.6 0 16.4

Schistura corica (Sc) (Hamilton, 1822) 0 0 0 15.5 19.5 0 3.2 55.5 0 6.3

Schistura devdevi (Sd ) Hora, 1935 0 0 0 10.2 20.2 0 1.6 60.2 0 7.8

Schistura savona (Ssa) (Hamilton, 1822)

0 0 0 9.5 16 0 2.1 61.2 0 11.2

Schistura scaturigina (Ssc) McClelland, 1839

0 0 0 8.6 12.5 0 5.2 55.9 0 17.8

Botia lohachata (Bl) Chaudhuri, 1912 0 0 0 0 29.2 0 0 61.8 0 9

Botia rostrata (Br)

Günther, 1868 0 0 0 0 24.5 0 0 55.6 0 19.9

Lepidocephalichthys guntea (Lg) (Hamilton, 1822)

0 0 1.3 30.1 0 29.4 0 20.4 0 18.8

Pseudecheneis sulcata (Ps) (McClelland, 1842)

0 0 0 0 10.2 15.2 0 52.2 0 22.4

Low altitude-

plain zone



19.2 0 17.5 0 0 15.6 0 24.5 0 23.2

Garra gotyla gotyla (Ggg) (Gray, 1830)

0 0 0 79.5 0 0 0 0 0 20.5

Garra lamta (Gl)

(Hamilton, 1822) 0 0 0 81.2 0 0 0 0 0 18.8


Amblyceps mangois (Amg) (Hamilton, 1822)

0 0 0 0 0 0 19.8 58.5 0 21.7

Olyra kempi (Ok)

Chaudhuri, 1912 0 0 0 5.2 39.8 0 0 40.2 0 14.8

Badis badis (Bb)

(Hamilton, 1822) 0 0 10 0 0 0 29.5 31.6 0 28.9



Altitudinal zones


River plains

Amblypharyngodon mola (Amo) (Hamilton, 1822)

5.2 7.4 0 59.5 0 10.2 0 0 0 17.7

Aspidoparia morar (Am) (Hamilton, 1822)

2.5 3.8 0 59.6 0 10.1 0 0 0 24

Bangana dero (Bd) (Hamilton, 1822) 0 0 0 75.2 0 15.2 0 0 0 9.6


Barilius barna (Bbr)

(Hamilton 1822) 0 0 0 0 0 0 0 79.2 0 20.8


19.2 0 17.5 0 0 15.6 0 24.5 0 23.2

Barilius vagra (Bv) (Hamilton, 1822) 13.5 0 19.2 0 0 16.1 25.6 0 25.6

Crossocheilus latius latius (Cl) (Hamilton, 1822)

2.5 5.6 0 10.2 0 61.8 0 0 0 19.9

Danio rerio (Dr)

(Hamilton, 1822) 0 0 0 0 10.6 0 15.2 63.5 0 10.8

Devario devario (Dd) (Hamilton 1822) 0 0 0 31.5 0 0 0 45.6 0 22.9

Devario acuticephala (Da) (Hora, 1921)

0 0 0 12.5 0 0 0 79.5 0 8

Esomus danricus (Ed) (Hamilton 1822)

0 0 0 0 15.2 0 0 38.5 0 46.3

Garra annandalei (Ga) (Hora, 1921) 0 0 0 87.6 0 0 0 0 0 12.4

Garra lamta (Gl)

(Hamilton, 1822) 0 0 0 81.2 0 0 0 0 0 18.8

Labeo pangusia) (Lp)

(Hamilton 1822) 0 0 0 7.5 0 84.2 0 0 0 8.3

Neolissochilus hexagonolepis (Nhx) (McClelland, 1839)

0 0 0 60.2 7.5 0 0 15.3 0 17

Pethia ticto (Pt)

(Hamilton, 1822) 0 1.2 6.8 38.3 0 0 0 20.5 0 33.2

Psilorhynchus sucatio (Ps) (Hamilton 1822)

0 0 0 80.5 0 0 0 5.5 0 14

Puntius conchonius (Pc) (Hamilton, 1822)

0 1.2 3.5 35.5 0 0 0 33.5 0 26.3

Pethia phutunio (Pp) (Hamilton, 1822) 0 0 0 29.5 0 1.2 4.5 31.2 0 33.6

Puntius sarana (Ps) (Hamilton, 1822) 0 2.5 4.5 39.2 0 0 0 30.5 0 23.3

Puntius sophore (Ps) (Hamilton 1822) 0 0 12.5 49.5 0 0 0 7.5 0 30.5

Puntius terio (Pt)

(Hamilton, 1822) 0 0 0 75.5 0 0 0 7.5 0 17

Rasbora rasbora (Rr) (Hamilton 1822)

5.2 1.2 9.5 35.6 0 0 1.3 30.2 0 17

Salmophasia bacaila (Sb) (Hamilton, 1822)

1.2 3.9 1.3 39.6 0 0 0 30.9 0 23.1

Salmophasia phulo (Sp) (Hamilton 1822)

0 0 0 30.5 0 0 15.2 40.2 0 14.1

Acanthocobitis botia (Ab) (Hamilton, 1822)

0 0 0 12.5 0 0 10.5 60.6 0 16.4


Schistura savona (Ss) (Hamilton, 1822)

0 0 0 9.5 16 0 2.1 61.2 0 11.2

Schistura scaturigina (Ssc) McClelland, 1839

0 0 0 8.6 12.5 0 5.2 55.9 0 17.8

Botia lohachata (Bl) Chaudhuri, 1912 0 0 0 0 29.2 0 0 61.8 0 9

Canthophrys gongota (Cg) (Hamilton, 1822)

0 0 0 0 21.2 0 19.5 48.5 0 10.8



Altitudinal zones


Lepidocephalichthys berdmorei (Lb) (Blyth, 1860)

0 0 0 25.6 0 15.2 0 26.1 0 33.1

Lepidocephalichthys guntea (Lg) (Hamilton, 1822)

0 0 1.3 30.1 0 29.4 0 20.4 0 18.8

Amblyceps mangois (Am) (Hamilton, 1822)

0 0 0 0 0 0 19.8 58.5 0 21.7

Batasio tengana (Bt) (Hamilton, 1822) 0 0 20 30 0 0 0 40 0 10

Mystus bleekeri (Mb)

(Day 1877) 0 0 0 0 31.2 0 19.2 36.5 0 13.1

Mystus tengara (Mt) (Hamilton, 1822) 0 0 0 0 29.8 0 21 35 0 14.2

Chaca chaca (Cc) (Hamilton 1822) 0 0 0 0 0 0 0 12.5 51.2 36.3

Hara horai (Hh)

Misra 1976 1.2 0 0 30 0 0 0 39.8 0 30.2

Pseudolaguvia ribeiroi (Pr)

(Hora 1921) 0 0 0 0 31.2 0 0 36.7 3.2 28.9

Pseudolaguvia foveolata (Pf) Ng, 2005 0 0 0 0 35.2 0 0 39.2 5.1 20.5

Olyra kempi (Ok)

Chaudhuri, 1912 0 0 0 5.2 39.8 0 0 40.2 0 14.8

Olyra longicaudata (Ol) McClelland, 1842

0 0 0 4.8 38.4 0 0 41 0 15.8

Ompok pabda (Op) (Hamilton, 1822) 0 0 0 3.2 40.2 0 0 39 0 17.6

Bagarius yarrelli (By)

(Sykes 1839) 0 0 0 0 45.2 0 0 35.6 10.2 9

Glyptothorax indicus (Gi) Talwar, 1991 0 0 0 0 41.6 0 0 39.5 0 18.9

Glyptothorax telchitta (Gt) (Hamilton 1822)

0 0 0 0 45.5 0 0 39.2 0 15.3

Glyptothorax cavia (Gc) (Hamilton, 1822)

0 0 0 0 38.9 0 0 42.1 0 19

Glyptothorax conirostris (Gc) (Steindachner, 1867)

0 0 0 0 35.2 0 0 39.5 0 25.3

Gogangra viridescens (Gv) (Hamilton, 1822)

0 0 0 45.8 0 20.1 0 0 0 34.1

Chanda nama (Cn) Hamilton, 1822 0 0 0 61.5 0 15.9 0 0 0 22.6

Parambassis lala (Pl) (Hamilton, 1822)

0 0 0 10.2 0 0 0 71.2 0 18.6

Badis badis (Bd)

(Hamilton, 1822) 0 0 10 0 0 0 29.5 31.6 0 28.9

Channa gachua (Cg) (Hamilton, 1822) 0 0 0 0 0 28.5 0 0 0 71.5

Channa marulius (Cm) (Hamilton, 1822)

0 0 0 0 25.2 0 0 45.2 0 29.6

Channa punctata (Cp) (Bloch, 1793) 0 0 0 0 39.5 0 0 35.6 0 24.9

Channa stewartii (Cs) (Playfair, 1867) 0 0 0 0 36.2 0 0 31.5 5.9 26.4

Glossogobius giuris (Gg)

(Hamilton 1822) 0 0 5.2 32.5 2.5 0 10.2 35.2 0 14.4

Trichogaster fasciata (Tf)

Bloch & Schneider, 1801 0 0 5.3 31.5 0 2.9 11.2 36.8 0 12.3

Trichogaster lalius (Tl) (Hamilton, 1822)

0 0 0 15.2 39.1 0 10.2 35.1 0 0.4

Macrognathus pancalus (Mp) Hamilton 1822.

0 0 0 15.3 0 0 0 45.2 0 39.5

Mastacembelus armatus (Ma) (Lacepède, 1800)

0 0 0 0 0 0 0 8.5 0 91.5

Monopterus hodgarti (Mh) (Chaudhuri, 1913)

0 0 0 10.3 31.2 0 0 30.2 0 28.3



Altitudinal zones


Xenentodon cancila (Xc) (Hamilton, 1822)

0 0 0 35.5 0 15.2 0 32.5 0 16.8

Barilius tileo (Bt)

(Hamilton, 1822) 12.5 0 15.5 0 0 18.9 0 21.6 0 31.5

Labeo angra (La)

(Hamilton, 1822) 5.2 0 4.5 45.5 0 0 0 0 0 44.8

Puntius ticto (Pt)

(Hamilton, 1822) 0 1.2 6.8 38.3 0 0 0 20.5 0 33.2

Raiamas bola (Rb)

(Hamilton, 1822) 0 10.2 12.5 20.5 0 0 0 29.8 0 27

Lepidocephalichthys annandalei (La)

(Chaudhuri, 1912) 0 0 0 29.8 0 18.2 0 27.5 0 24.5

Parambassis ranga (Pr)

(Hamilton, 1822) 0 0 0 5.2 0 0 0 75.5 0 19.3

Macrognathus aral (Ma)

(Bloch & Schneider, 1801) 0 0 0 0 0 0 0 55.2 0 44.8

Aspidoparia jaya) (Aj)

(Hamilton, 1822) 1.2 5.9 0 61.5 0 9.2 0 0 0 22.2

LV: leaves; FR: fruits; HR: higher plants; AL: Algae; TI: Terretrial insects; PL: Planktons; CR: crusteceans; AI:

aquatic insects; FI: Fish; DU: detritus and unidentified food materials.

IN: Insectivore; AL: Algaevore; H: Herbivore; PL:

Planktivore; MIC: Micro-Carnivore; MAC: Macro-

Carnivore; O: Omnivore; D: Detritivore

Fig. 2 Proportional composition (by frequency) of

major prey items (feeding guilds) of species at

respective altitudinal zones.

Environmental stimulants in functional group

structure

Environmental characteristics (Table. 3) were

measured for Dissolve Oxygen (DO), Temperature

(WT & AT), pH, Conductivity (CON), Turbidity (TUR)

and Water current (WC). The positions of the

environmental vectors indicate their correlation to

the axes as well as to each other. Canonical

component analysis (CCA) ordination graph (Fig. 3)

showed that the major fish assemblage groups based

on their feeding habits along longitudinal gradient of

River Teesta in West Bengal are positively correlated

air and water temperatures. As temperature is one of

the main deterministic factors for altitudinal

variations of fish communities based on their

functional traits, we have analyzed as to whether

altitude has any role/effect in composing fish trophic

groups along different habitat types. The canonical

axes 1 and 2 (Eigenvalues = 0.62 and 0.35) explained

70.1% of the cumulative variance of the species data,

while they explained 70.6% of the cumulative variance of

the species–environment relation. Out of the seven

variables used in the model, air and water temperature

were found to be most significant (p < 0.05).



Table 3. Environmental Parameters of River Teesta.

pH Air temp.

(°C) Water

Temp. (°C) DO

(mg/lt) Turbidity

(ppm) Conductivity

(µS/cm)

Water velocity (m/sec)

Rishi Khola Avg±SE 7.38 ±0.16 22.25±1.14 19.52±0.92 7.94±0.10 43.02±1.78 99.35±0.34 1.16±0.13

range 7.2-7.6 21-23.7 18.5-21 7.9-8.1 41.2-45.4 99-99.9 1.1-1.4

Rungpo Avg±SE 7.13±0.09 22.98±1.06 20.10±0.51 7.69±0.07 43.93±1.24 98.23±1.12 1.07±0.10

range 7.02-7.3 21.1-24.5 19.5-21 7.6-7.8 42.7-45.8 96.8-99.6 0.9-1.2

Teesta Bazar

Avg±SE 7.07±0.07 25.72±1.13 22.53±1.92 7.56±0.10 43.14±1.52 107.10±3.21 1.14±0.15

range 7.01-7.2 24-27 20.7-24.9 7.4-7.7 41-45.1 100.7-109.3 0.9-1.4

Sevoke Avg±SE 7.19±0.09 22.57±2.60 17.03±0.99 7.28±0.11 76.78±1.24 110.93±0.78 1.40±0.11

range 7.1-7.3 18.5-25.2 15.4-18.5 7.1-7.4 75.3-78.9 110-112.3 1.3-1.6

Gojoldoba Avg±SE 7.28±0.17 32.82±2.04 29.52±1.01 7.09±0.07 73.28±1.68 110.85±0.81 1.71±0.10

range 7.14-7.5 30.1-35.5 28.2-31 7.01-7.2 70.6-75.1 109.6-112.1 1.6-1.9

Domohoni Avg±SE 7.72±0.43 35.02±0.57 30.47±0.31 6.99±0.12 71.18±0.90 114.73±1.20 2.16±0.21

range 7.3-8.5 34-35.7 30.1-31 6.8-7.1 70.2-72.5 113.7-117 1.9-2.2

Haldibari Avg±SE 7.56±0.11 35.38±1.32 30.53±0.53 6.95±0.11 76.32±1.34 117.20±2.21 2.40±0.36

range 7.4-7.7 33.7-37.2 29.9-31.1 6.8-7.1 74.8-78 113-119 2.1-2.9

Fig. 3 CCA plot showing species scores along

environmental vectors.

Altitudinal comparisons of dietary compositions

Distinct differences in dietery regime in relation to

habitat use were detected. At the habitat level, four

major zones were separated according to their

altitude and water temperature regime. Cluster

analysis was attempted to group various zones along

the longitudinal gradient of River Teesta in West

Bengal based on the dietary regime of the available

species in respective zones. Fig. 4 shows the results of

a hierarchial clustering using individual species

linking on data sampled during December 2010 to

March 2013 in 7 sites representing the longitudinal

gradient of River Teesta at Darjeeling and Jalpaiguri

districts in West Bengal. The raw data were expressed

as % frequency of availability of prey items of 92 fish

species at respective sites, and Bray-Curtis

similarities calculated on √√-tranformed frequencies.

The dendogram provides a sequence of fairly

convincing groups; two groups (determined at 50 %

similarity level) have been obtained. One group forms

the high-mid altitude zones viz. Rishi Khola, Rungpo,

Teesta bazaar and Sevoke while the other group

segregated as the river plain one viz. Gojoldoba,

Domohoni and Haldibari. Hence, it is observed that



altitudinal variations influence the resource

availability and dietary composition of species

obtained at each sites. However, a cluster analysis is

not adequate enough to give a complete and jointed

picture of the trophic group pattern. It is not clear

from the dendogram alone whether there is any

natural sequence of community change across the two

main clusters. In fact, there is a strong dietary shift

across the region, associated with changing altitude

and habitat conditions. This is best seen in an

ordination of the diets of the 92 fish species at

respective sites (Fig. 5). There is a greater degree of

variability of the feeding habit nature and hence the

changing community composition with altitude and

temperature. Evident is a marked change in

composition between Rungpo (high altitude) and

Gojoldoba (plains). One-way ANOSIM demonstrated

the influence of the factor “altitude”. The overall

dietary compositions differed to a greater extent

among species at respective zones with P<0.001 in

most of the cases. Similarity profile (SIMPROF) test

have been carried out on the MDS ordination of the

altitudinal zones, based on the diet regime of the fish

communities (Fig. 6). The dendrogram displays one

group (dashed lines) structure for which there is no

evidence from a SIMPROF test, and the other group

(continuous lines) being used for divisions for which

SIMPROF rejects the null hypothesis (that samples in

that group have no relation to habitat types). Dashed

lines indicate groups of samples not separated (at

P<0.05) by SIMPROF. The dashed line groups forms

the species that belong to a single altitudinal zone viz.

mostly the river plains, whereas the continuous lines

forms the species that belong to different zones

indicative of distinct groups of species filtered

through feeding habits in perspective of altitudinal

variation.

Fig. 4 Similarity dendogram for hierarchial

clustering of sites constitutive of respective altitudinal

zones showing linking of Bray-Curtis similarities

calculated on obtained feeding groups at each site.

Fig. 5 Two-dimensional MDS ordination plot of the

volumetric dietary data for respective fish species

coded for habitat/altitudinal gradient.

Fig. 6 Sequence of SIMPROF tests on dendrogram

from standard hierarchical clustering based on the

diet composition fish species.



Discussion

This study demonstrated the overall dietary

compositions of the ninety-two species collected and

identified along the longitudinal stretch of River

Teesta. Aquatic insects are being consumed as the

main dietary constituent as has been observed from

the dietary composition of the species. This pattern

has been observed in hilly streams by many other

authors outside India (Motta and Uieda, 2004; Uieda

and Motta, 2007; Winemiller et al., 2008; Vidotto-

magnoni and Carvalho, 2009; Ferreira and Casatti,

2006; Rocha et al., 2009). However, any such

documentation in Teesta River, India is lacking.

Detritus was also a large part of the diet of the fish

assemblages, which generally occurs in higher in

impacted streams. The specific diets of each species

were related to their distinct feeding habits and use of

stringent habitats. The effects of shared resource used

and competition that might occur in locations where

the food supply is limited to a few sources is

intensified by this factor. Therefore, the patterns of

use of a specific range of food resources by the high

altitude species is probably not related to food overlap

or competition, but to the abundance of specific

aquatic invertebrates limited to this specific zone.

Hence we observed that the high-mid altitude zones

were mainly dominated by the loaches (Danio rerio,

Schistura devdevi and Schistura savona) and cold

water carps (Schizothorax richardsonii and Tor tor)

having specific diet requirements. Further

downstream, where the river hits the plain, both the

availability and respective abundance of food

resources increased (in view of higher water

temperature, lesser water current and muddy river

beds, providing a favorable and productive habitat for

a variety of organisms) resulting in the dominance of

omnivores species (Rasbora rasbora, Salmophasia

phulo, etc). As such, analysis of the food composition

in perspective of the main habitat occupation and

activity patterns of some species, suggested ecological

segregation existed among species within the

community. Further the field observations indicated

habitat segregations among overlapping species,

suggesting that food partitioning mechanisms may

occur at different levels with environment being a

major filtering agent. Our result support that habitat

segregation explained the observed co-existing

pattern with environmental factors determining the

occurrence of specialized species such as loaches

(Schistura spp.) at certain stations; as has been

observed by other authors (Costa de Azevedo et al.,

2006; Mouillot et al., 2006).

Apart, as observed in a Panamanian stream (Zaret

and Rand, 1971), the results show that despite

hydrological variation produced year round in the

form of spates, habitat modifications do not seem to

be sufficient to produce drastic changes in food

niches. However, in the present study, habitat

modification somewhat seems to effect the pattern of

resources utilization and the occurrence of resident

fish community. This was seen in the increase of

omnivorous species at both somewhat anthropogenic

disturbed sites (Teesta bazaar and Sevoke). Although

these sites form the high-mid altitude zones of the

River Teesta, here omnivorous species seems to be

equally abundant as insectivores. This may be due to

the fact that disturbances (dam construction and

movement of heavy vehicle over the river bed) at

these sites have led to lesser availability of the specific

aquatic insect prey items. As such species might have

shifted to higher variety of resource utilization. This

flexibility accounts for the ability of these species

(Barilius spp. and Lepidocephalichthys spp.) when in

altered habitats, to feed on suites of prey that vary

significantly in their compositions and to flourish in

those habitats. Studies (Hourston et al., 2004) have

shown that differences in the diets of Atherinomorus

ogilbyi, S. schomburgkii and L. platycephala among

the different habitat types, which differed in the

extent to which they were exposed to wave action,

could be related to differences in the relative

abundances of their different potential prey. This is in

consistent to the present study which accounts for the

differences and or specificity of the potential prey,

owing to temperature, water velocity and substrate

variations at respective zones which intensifies

altitude as one of the main factor in determining



species assemblage pattern and resource utilization.

In context, habitat segregation, however was observed

among most of the species, suggesting some degree of

food partitioning exists in hill-stream species.

Beside, other authors have found that most of the

food resources consumed by stream fish are of

allochthonous origin (Castro, 1999; Esteves and

Aranha, 1999; Lowe-mcconnell, 1999; Alvin and

Peret, 2004). In the present study, although both

allochthonous and autochthonous resources were

used by fish assemblages, autochthonous resources

dominated the diet of most species. This was also

observed in studies performed by Rondineli et al.

(2011) and Bonato et al. (2012). This may be in view

of the fact that terrestrial insects and vegetal

fragments were only consumed during the rainy

season which consisted of a large area within riparian

vegetation. Therefore, low contribution of

allochthonous items can be explained by the

disruption of riparian vegetation in the studied areas.

As opined by many authors (Angermeier and Karr,

1983; Rezende and Mazzoni, 2005; Tófoli et al., 2010)

normally, the input of allochthonous material from

both plants and animals in aquatic environments is

greater in the rainy season, mainly because of the

displacement of these organisms to the aquatic

environment by rain and wind and the leaching of

adjacent areas. The fish fauna of River Teesta is thus

mantained by a few resources, of which those of

autochthonous origin are fundamental for the

maintenance of the greatest part of fish biomass. The

small size of most of the species populations, the high

number of habitat-specific species and the direct and

indirect dependence of food sources that derive from

the forest, suggest that the fish populations of this

clear water river of the eastern Himalayan

biodiversity hotspot region might be very sensitive to

habitat alteration. Hence, future studies which will

aim to assess anthropogenic impacts and prioritize

conservation efforts are strongly recommended.

Acknowledgements

The authors are highly grateful Shri K.C.Gopi,

Scientist-E, Zoological Survey of India, Kolkata for

guidance, support and research facilities in the

taxonomic study. We are also indebted to the local

fishermen of Jalpaiguri and Darjeeling districts of

West Bengal for assistance in experimental fishing

and providing necessary amenities. Financial

assistance provided by Council of Scientific and

Industrial Research (CSIR) to Munmun Chakrabarty

is gratefully acknowledged.

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